I have a main program which has a button Authenticate. On click of authenticate open a form for auth which has USERNAME FIELS AND PASSWORD.
If entered fields are true then enable editing of jtable in main program..

Basically something like this :
//main program
Authenticate.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent ae)
{
UpdateAuth ua=new UpdateAuth();// opens form which has username and pass for authentication
ua.setVisible(true);

I have a main program which has a button Authenticate. On click of authenticate open a form for auth which has USERNAME FIELS AND PASSWORD.
If entered fields are true then enable editing of jtable in main program..

Well, you might be in over your head.

//need code here for enabling table
if(s=="mactus")

If you don't know how to correctly test for String equality, you will have no chance of getting this to work.

You need to hit the tutorials. First the basic one, then the Swing one.